1. Field of the Invention
The present invention relates to embedded heater wires, and more particularly, shielded, embedded heater wires.
2. Description of the Related Art
An embedded heater wire is generally an insulated, electrically conductive heater wire which is embedded into and just below a surface such as a door, wall or floor which is to be heated thereby. A shield consisting of a number of very fine copper wires is usually woven around the insulation which surrounds the heater wire. The grounded shield is a safety device which protects the external apparatus from the heater wire in the result of a failure of the insulation. The shield can be connected to a ground-fault interrupter which, when sensing leakage current within the shield originating from the heater wire, switches off power to the heater wire. It is desirable to measure the temperature of the heater wire and/or the heated substrate while in operation in order to monitor the heater's performance and to guard against fire hazards.
It is known to measure the temperature of a heater wire by directly contacting the heater wire with a temperature probe somewhere along its length. A problem is that the heater wire is embedded while in use and it is sometimes necessary to compromise the integrity of either the heated surface or the insulation surrounding the heater wire in order to insert a temperature probe against the heater wire. Another problem is that such heater wires typically carry high current during operation, and any exposure of the heater wire creates a shock hazard.
It is also known to measure the temperature of the surface being heated by embedding temperature sensors therein and/or placing temperature sensors thereon. A problem is that embedded sensors structurally weaken the heated substrate. Sensors placed upon the surface may be unaesthetic or damaged by foot traffic. Another problem is that wires must be extended from the sensors to a central electrical processor. The sensors and associated wires also represent an additional expense.
What is needed in the art is a heater wire apparatus in which the temperature of the heater wire and/or heated substrate can be determined without exposing or making direct contact with the heater wire itself and without the need for additional temperature sensors.